Recently, the tunneling magnetoresistance (TMR) mechanism has been widely employed for magnetic random access memory (MRAM) and magnetoresistance sensor applications. For example, a tunneling magnetoresistance sensor is frequently used as a rotary position sensor to sense an angular variation with high accuracy. Due to its higher magnetoresistance ratio and higher electrical resistance than a typical giant magnetoresistance (GMR) sensor, the TMR sensor has shown benefits in higher output signal, wider detection airgap and lower power consumption.
A conventional TMR device is based on the magnetic tunnel junction (MTJ) design, which comprises two ferromagnetic layers (a top ferromagnetic layer and a bottom ferromagnetic layer) separated by a thin tunnel dielectric layer. The magnetoresistance is read by applying an electric current vertically through the top ferromagnetic layer, the tunnel dielectric layer and the bottom ferromagnetic layer. In other words, the electric current has a flow direction perpendicular to the normal plane of the TMR device and conducts an upper electrode and a lower electrode adjacent to the top and the bottom ferromagnetic layers, respectively. Thus, the magnetoresistance sensor using such current conduction mode is called a current-perpendicular-to-plane tunneling magnetoresistance (CPP-TMR) sensor.
However, because the upper electrode and the lower electrode are spatially arranged on both sides of the CPP-TMR sensor, it means two metal layers are required in the structural design and the manufacturing process, which are more complicated compared with those of conventional AMR and GMR sensors.